What is this weed?

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It has popped up in our lawn and vegetable patch. Red stalk with two boat shaped leaves and a thin white root. About two inches tall in total.

picture on my profile (tried to post it here, but didn't work)

I think you have to make your profile public. I've seen dock with red stalks before, could it be that?

Done that now. Any ideas?

Ruby chard has red stalks, but I'm not suggesting it's edible!

I think it might be a sycamore seedling.

SisterMoonshine: that is brilliant! I think you are right. We have two huge sycamore trees in the garden and one smaller one, and they obviously are trying to spread... Funny how the shape of the leaves is so different!
We seem to have thousands of seedlings in the garden.

Yes Sycamore. Hoe them off and leave them to dry up on the surface of the soil before they get too big.

I think the next leaves that come will have the sycamore shape.
I have sycamores around too and seedlings popping up that look like yours.

Yes - sycamore: all the MN gardeners been commenting on them this year!

The seedlings of most plants start off with the cotyledons (the food store within the seed) forming the first 'seed leaves', to get the plant going, before the proper leaves develop. If you have other similar seedlings, watch them for a week or two and you will see the typical sycamore leaves emerge.

Or if you grow one in a pot, and look after it carefully, you might be able to 'bonsai' it.